Tun-Tap devices are used by e.g. OpenVPN software. CRIU has support for them.
DevicesEdit
The netdevice entry sits in netdev-ID.img image file and has optional tun field.
FilesEdit
Other than this there's always a reg-file entry in the images for tun deivce. In addition to this there's an entry in the tunfile image. The device-to-file mapping is performed by device name.